A hang on sloopy is a turd that doesn't want to be detached whilst its being laid. Made famous by the McCoys in their 1965 song "Hang on Sloopy", detailing a turdtastic sexual encounter with poo the lead singer had earlier that year.

Annotated original lyrics are below:

Sloopy lives in a very bad part of town
(His ass, of course.)
And everybody yeah, tries to put my Sloopy down
(Who wouldn't? Sloopy is a turd.)
Well, Sloopy I don't care what your daddy do
Cause' you know Sloopy girl I'm in love with you
(Part scat, part fecaphiliac incest.)

Hang on Sloopy, Sloopy hang on
Hang on Sloopy, Sloopy hang on
(He's laid his Sloopy, but it's hanging on his ass. He can't shake it off.)

Sloopy let your hair down girl, let it hang down on me
Sloopy let your hair down girl ,let it hang down on me
(Observation that the Sloopy has hair in it. Vile.)